In recent years, the demand for high-speed, lower power consumption and large-capacity non-volatile memories has increased. Promisingly the memristor can be used due to its special characteristic of having memory through resistance change. The memristor behavior is not limited to digital applications, but it can be used in analog application as well including: memristors in chaotic circuits, amoeba's learning, neural synaptic emulation, reprogrammable and reconfigurable circuits, and for neuromorphic computers. On the other hand, Micro Electro Mechanical Systems (MEMS) are small scale structures that can interact with the physical world due to their mechanical properties. These devices are widely used in diverse applications such as: accelerometers, pressure sensors, micro-optics, biosensors, tilting mirrors, and RF switches. One of the most common MEMS devices is the electrostatic actuator which moves a metal electrode when a voltage is applied; however, these actuators are limited to one third of its gap. The purpose of this work is to investigate the potential of the integration of these two devices and extend the application branch of the memristor.
Microelectromechanical System (MEMS) devices have wide application for sensing and actuation. One of the most common and versatile MEMS devices are parallel plate capacitors. For example, they are used as accelerometers in automobiles for airbag deployment and gyroscopes for mobile smartphones. The device is composed of two electrodes (upper and bottom) separated by a gap.
When a voltage is applied across the bottom and upper electrodes, an attractive electrostatic force will move the upper electrode (which is free to move) towards the bottom electrode (which is fixed). However when the separation between electrodes is reduced to less than ⅔ of the original gap, an unstable situation occurs which causes the upper electrode to collapse with the bottom electrode. This effectively reduces the operating range of the capacitor to ⅓ of the possible motion. If the position of the upper electrode could be sensed, that signal could be used in a closed-looped control circuit to dynamically control the position and extend the operating to 95% of the full range of motion. However, the main issue with closed-loop control is the lack of a suitable method for sensing the position of the upper electrode.
On the other hand, memristor-like devices can be employed in different applications including digital and analog electronics. Within these applications are high-density non-volatile memories, neural synaptic emulation, and neuromorphic computers. The device consist of two electrodes separated by an insulator. When a voltage is applied across the electrodes, the resistance in the insulator changes. Due to this behavior the memristor can be used in diverse applications, however, the integration of this device with other circuit element is still under development. This invention employs the memristor in a new application, where this device is integrated with the MEMS capacitor in closed-loop control system to accurately sense the position of the upper electrode. This will extend the MEMS operating range to 95% for a wider range of sensing and actuation applications.